1. Field of the Invention
The present invention relates to a secondary cell.
2. Description of Related Art
Recently, lithium-ion secondary cells with high energy density (Wh/kg) have been developed as a power source for hybrid vehicles, electric vehicles, and the like, and among them prismatic secondary cells with high volumetric energy density (Wh/L) are brought to the attention.
For prismatic lithium-ion secondary cells, there has been proposed a method in which a flat-shaped electrode roll is prepared by winding a positive electrode sheet where a positive electrode is coated on a positive foil, a negative electrode sheet where a negative electrode is coated on a negative foil, and an insulating separator, and an uncoated positive foil and an uncoated negative foil are exposed at the axial ends of the electrode roll so as to connect each of the exposed portions with a current collector plate.
Japanese Laid Open Patent Publication No. 2005-216825 discloses a structure in which a U-shaped current collector plate is inserted inside the winding of a winded body and the exposed portion is divided into two so as to connect each of them with a current collector plate. This allows the exposed portion to be reduced in width, which is advantageous in reducing a cell in size.